Hydraulic jet drill bit

ABSTRACT

A drill bit for the drilling of wells by the hydraulic jetdrilling method in which a plurality of nozzles slope downwardly through the lower end of the drill bit in a direction having a component opposite the desired direction of rotation of the drill bit. The drill bit is rotatably mounted on the lower end of the drill string whereby the drill bit rotates independently of the drill string as a result of the reaction from streams of drilling liquid discharged at high velocities from the nozzles.

Unite States Patent Willard P. Acheson; Gerald H. F. Gardner, Pittsburgh; Joseph H. Messmer, O'Hara Township, Allegheny inventors [56] References Cited UNITED STATES PATENTS 1,766,487 6/1930 Conner 175/422 2,218,130 10/1940 Court 175/422 3,266,577 8/1966 Turner 166/222 3,326,607 6/ 1967 Book 175/67 3,324,957 6/1967 Goodwin et al..... 175/422 3,414,070 12/1968 Pekarek 175/422 Primary Examiner-James A. Leppink Attorneys-Meyer Neishloss, Deane E. Keith and Paul L.

Tillson ABSTRACT: A drill bit for the drilling of wells by the hydraulic jet-drilling method in which a plurality of nozzles slope downwardly through the lower end of the drill bit in a direction having a component opposite the desired direction of rotation of the drill bit. The drill bit is rotatably mounted on the lower end of the drill string whereby the drill bit rotates independently of the drill string as a result of the reaction from streams of drilling liquid discharged at high velocities from the nozzles.

ll 1' E1 36 l is f A48 12 i M 12 l 50 3 /llll L HYDRAULIC JET DRILL air This invention relates to drilling and more particularly to a drill bit for use in the hydraulic jet drilling of wells.

ln rotary-drilling processes widely used for the drilling of oil and gas wells, a drilling liquid is circulated down a rotating drill string and out through ports in a drill bit attached to the lower end of the drill string. The drill bit is forced downwardly against the bottom of the borehole by heavy drill collars that form a part of the lower end of the drill string whereby the formation being drilled is crushed or cut mechanically by elements on the bit. Drilling liquid discharged from the bit suspends cuttings of the formation penetrated and carries them upwardly through the annulus surrounding the drill stem to the upper end of the borehole.

The conventional rotary-drilling operation in which the cutting of the formations penetrated is by mechanical contact of cutting or crushing elements on the bit has been highly successful in drilling soft formations and formations of medium hardness. Rotary drilling, however, has not been as successful in drilling through hard rock. The slow rates of penetration of the rock and the relatively rapid wear of the drill bits have contributed to making conventional rotary drilling through hard rocks very expensive.

A recently developed method that has been effective in drilling hard rock is hydraulic jet drilling in which a drilling liquid having abrasive particles suspended in it is discharged through nozzles in the drill bit at high velocities against the bottom of the borehole. Drilling liquid velocities of at least about 650 feet per second are used in hydraulic jet drilling. Penetration of the rock is the result of erosion or dislodgement of particles of rock by impingement of the abrasive particles against the rock. The drill bit is mounted on the lower end of drill pipe and rotated in the hole at a rate ordinarily in the range of 30 to 100 r.p.m. to cause jet streams discharged from the nozzles to travel over the bottom of the borehole to cut the rock forming the bottom of the borehole. Concentrations of the abrasive used in the jet-drilling process depend upon the type of abrasive used. Drilling rates increase with an increase in the concentration of the abrasive until the abrasive concentration is high enough to cause interference of one abrasive particle with another.

We have found that the drilling rate can be increased by optimum spacing of the points of impact of abrasive particles against the bottom of the borehole. The spacing is greater than the spacing that is obtained with abrasive concentrations'and rates of rotation usually used in hydraulic jet drilling. However, the abrasive concentration has a larger effect on drilling rate than the spacing, and reduction of the abrasive concentration to obtain the desired spacing results in a reduced drilling rate.

This invention relates to a drill bit mounted on the lower end of nonrotating drill pipe used to drill a well. A plurality of nozzles slope downwardly through the lower end of the drill bit at an angle having a horizontal component opposite the direction of rotation of the drill bit. The reaction from the high-velocity stream of drilling liquid causes rotation of the drill bit at a rate in the range of 500 to 2,000 r.p.m. In a preferred embodiment of this invention a centrally positioned standoff element extends downward from the lower surface of the drill bit to cut a central hole and support the drill bit a short distance above the bottom of the borehole.

IN THE DRAWINGS FIG. 1 is a longitudinal sectional view diagrammatically illustrating the drill bit of this invention.

FIG. 2 is a horizontal sectional view along section line Il-II in FIG. 1 showing the position of some of the nozzles in the drill bit of this invention.

Referring to FIG. 1 of the drawings, drill string is shown with the drill bit of this invention secured to its lower end. Drill collars may form the lower part of the drill string, but because of the very low weight put on the bit of this invention drill collars ordinarily will not be necessary and the drill string 10 will include only drill pipe running from the upper end of the hole downwardly to the drill bit. Drill string 10 is connected at its upper end in any manner, not shown in the drawings, with the discharge end of high-pressure pumps used to deliver the drilling liquid under high pressure, such as 4,000 p.s.i. or more, into the upper end of the drill string 10. Abrasive particles such as ferrous abrasive or sand are suspended in the drilling liquid to aid in cutting the formations drilled. Additives such as wood fiber, asbestos fiber and/or clay may be added to the drilling liquid to increase its ability to suspend the abrasive and the particles cut from the formation during the drilling operation, or to modify other characteristics of the drilling liquid as desired.

The lower end of drill string 10 is externally threaded to receive a housing 12 in which a cylindrical drill stem 14 is rotatably mounted. Drill stem 14 has an upper shoulder 16 and a lower shoulder 18 on its external surface to receive bearings 20 and 22, respectively, that rotatably support the drill stem within housing 12. An annular ledge 24 extending inwardly from the housing 12 above the upper bearing 20 supports packing 26 in the space between the drill stem 14 and the housing 12. Lubricants are introduced into the packing through a check valve 28 mounted in the wall of the housing. A bushing 30 bears against the upper end of packing 26 to compress the packing between the drill stem 14 and housing 12. Bushing 30 is held in place on a shoulder 32 on the inner surface of housing 12 by an expansion ring 34.

Lower bearing 22 is held in place by a lower bushing 38 screwed into the lower end of housing 12. the lower end of bushing 38 is spaced from the drill stem 14 to provide a stuffing box 40 into which a packing gland 42 extends to compress packing and thereby provides a seal preventing leakage of drilling liquid into the bearings 20 during the drilling. Lubricants are introduced into the bearings through a fitting 36 mounted in the wall of the housing; the volume between the bearings is arranged to hold sufficient lubricant for normal periods of operation.

The lower end of drill stem 14 is externally threaded to receive a shank 44 of a drill bit, indicated generally by reference numeral 46, constructed in accordance with this invention. Shank 44 extends downwardly to a hollow body 48 closed at its lower end by a bottom member 50. A backsplash plate 52 of hard, abrasion-resistant material, such as a tungsten carbide alloy, is secured to the lower surface of bottom member 50.

A plurality of nozzles 54 extend downwardly through the bottom member 50 and backsplash plate 52 of drill bit 46. The outlets of nozzles 54 are substantially in the plane of the lower surface of the backsplash plate. It is essential to this invention that the plurality of nozzles 54 slope downwardly in a direction having a component in a direction opposite to the desired direction of rotation of the drill bit 46, and that either no nozzles slope downwardly in the direction of rotation of the drill bit or the number of nozzles sloping in the direction of rotation is small enough that the reactive forces from those nozzles is overcome by the reactive force from nozzles sloping opposite the direction of rotation. Actually, nozzles sloping downwardly in the direction of rotation are detrimental to this invention in that they reduce the torque available to rotate the drill bit, and it is preferred that all of the nozzles slope to encourage rotation in the same direction. The nozzles may slope outwardly ,or inwardly as well as downwardly and in a direction opposite to the direction of rotation, as illustrated by nozzle 54a in FIG. 2. To provide an effective reaction force tending to rotate the drill bit, the slope of most of the nozzles sloping in a direction opposite the direction of rotation of the drill bit should be substantial, for example, at an angle of at least 20 with the vertical. The maximum slope is limited largely by the space available.

The nozzles 54 are positioned to impinge against substantially the entire bottom of the borehole as the drill bit rotates. The desired object of impinging against the entire bottom of zles, such as nozzles 5% and Me, on one radius and nozzles 5M, 54, and filf on another radius at different distances from from the center of rotation. The angles and directions in which the nozzles slope downwardly can also be varied to accomplish the desired object of impinging against substantially the entire bottom of the borehole in each revolution of the drill bit. Some of the nozzles, for example nozzle 54f, can be vertical.

While some of the nozzles, such as nozzle 54c, may slope inwardly toward the center of the drill bit, it is not desired to cut the center of the bottom of the borehole by means of highvelocity streams discharged from the nozzles. A standoff element 56 having a maximum horizontal length of about 1 inch and constructed of a hard, abrasion-resistant material such as a tungsten carbide alloy extends downwardly a distance of one-half inch to 1% inches from the backsplash plate 52 in the center of the drill bit. The standoff element 56 supports the drill bit the desired distance above the bottom of the borehole to maintain the proper standoff of the nozzle outlets from the bottom of the borehole. The small amount of rock in the central core left by the streams discharged from the nozzle is easily drilled by the standoff element 56. Because of the central position of the central core drilled by the standoff element 56, the torque required to drill the central core mechanically is small. Bars 58 extending downwardly from the bottom of the backsplash plate can be provided to break any small ridges that might be left by the hydraulic jet streams discharged from nozzles 54. Bars 58 should not extend downwardly as far as standoff element 56. It is desirable that bars 58 avoid contact with the bottom of the borehole, except for occasional contact with isolated thin ridges that may extend upwardly above the level of the main surface of the bottom of the borehole, and thereby avoid increasing the torque required to rotate the bit. Nozzles 54 are preferably constructed of a tungsten carbide alloy.

In a preferred nozzle design, the nozzle has an elongated tape ring entrance portion extending from the nozzle inlet to a cylindrical throat which extends to the nozzle outlet. The throat portion has a diameter in the range of approximately three thirty-seconds to three-sixteenths inch and a length of one-half to three-fourths inch. The entrance portion has a length of approximately lr to 4 /2 inches, and has convex surfaces having a radius of curvature preferably in the range of 50 to 70 inches. The nozzle design described above is merely a preferred nozzle design that has given extended nozzle life. Nozzles of other design can be use.

In the operation of the drill bit of this invention, drilling liquid containing abrasive particles suspended therein is pumped down the drill string under a high pressure of the order of 4,000 p.s.i. to 12,000 psi. If the abrasive suspended in the drilling liquid is ferrous shot or grit, a concentration of l to 10 percent by volume ferrous abrasive can be used. The drilling liquid passes through the screen 36 into the drill stem 14 and into the drill bit 46. The drilling liquid is then discharged at high velocities of 650 feet per second or more through the nozzles 54 against the bottom of the borehole. Because of the orientation of the nozzles sloping downwardly in a direction opposite to the direction of rotation of the drill bit, the reaction forces cause the drill bit and drill stem 14 to rotate within housing 12. It is desired that the drill bit rotate at a high speed, for example, at a rotation rate of 500 to 2,000 r.p.m. Excessive rates of rotation can be avoided by baffle plates 60 which extend from the shank 44 of the drill bit.

The number of nozzles that slope downwardly in a direction having a horizontal component in a direction opposite the direction of rotation will depend upon the size of the bit, the size of the nozzles, the orientation of the nozzles, and the pressure drop of the drilling liquid as it passes through the nozzle.

For example, drilling liquid discharged through a nozzle oneeighth inch in diameter inclined at 20 at a velocity resulting in a pressure drop.of 5,000 p.s.i, will provide approximately two horsepower which may be applied to rotate the bit. Five such nozzles should be more than adequate to rotate the bit at the desired speed in the absence of mechanical cutting of the rock. 20 nozzles is near the maximum number that could be positioned in a bit for drilling boreholes, for example of 7% inch diameter, for oil or gas wells. Because the small central core offers little resistance to turning the drill bit, and the load placed on the drill bit is little more than that required to maintain standofi element 56 in contact with the bottom of the borehole, 5 to 20 nozzles inclined to cause rotation can be used. A total weight on the bit of 500 pounds is adequate.

The drill bit of this invention provides a simple means for rotating a hydraulic jet drill bit at speeds well above those used in hydraulic jet drilling. By rotatably suspending the drill bit on the lower end of the drill pipe, the desired high rates of rotation are obtained without rotating the drill pipe. The drilling liquid is highly erosive because of the abrasive particles suspended in it. Erosion of turbine blades is eliminated in the drill bit of this invention.

We claim:

1. A drill bit for the hydraulic jet drilling of the borehole of a weld through hard formations comprising a hollow drill bit body, bearing means supporting said drill bit body on the lower end of drill pipe for rotation independently of the drill pipe, said drill bit body having a substantially flat bottom, a plurality of nozzles extending through the drill bit body for the discharge of liquid delivered into the drill bit body from the drill pipe, said nozzles sloping in the direction opposite to the desired direction of rotation of the drill bit whereby reaction of drilling liquid discharged from the nozzles rotates the drill bit body, said nozzles being positioned to cut substantially the entire bottom of the borehole other than a minor portion at the center of the borehole by drilling liquid discharged from the nozzles, and a standoff element centrally located on the bottom of the drill bit and extending downwardly therefrom a distance of one-half to 1% inches, said standoff element having a length adapted to engage only that minor central portion of the bottom of the borehole not cut by the drilling liquid.

2. A drill bit as set forth in claim 1 having 5 to 20 nozzles with the opening through the nozzles having a diameter in the range of three thirty-seconds to three-sixteenths inch.

3. A drill bit as set forth in claim 1 in which bars extend downwardly from the lower surface of the drill bit at a distance less than the standoff element and are adapted to break thin rock ridges that may extend upwardly from the bottom of the borehole.

d. A drill bit as set forth in claim 1 in which the drill bit body has a shank of smaller diameter than the drill bit body at its upper end and baffle plates extend radially from the shank.

5. A method of drilling a borehole of a well in hard formations comprising rotatably suspending a drill bit on the lower end of drill pipe extending down the well, pumping a drilling liquid having an abrasive suspended therein down the drill string to the drill bit at a pressure of at least 4,000 p.s.i., discharging the drilling liquid from the drill bit at a velocity of at least about 650 feet per second through 5 to 20 nozzles having a diameter of three-sixteenths to three thirty-seconds inch positioned to discharge drilling liquid against substantially the entire bottom of the borehole and sloping downwardly through the lower end of the drill bit in a direction having a component in the direction opposite the direction of rotation of the drill bit whereby reaction from the drilling liquid rotates the drill bit at a rate of 500 to 2,000 r.p.m., supporting the drill bit on the bottom of the borehole by a standoff element extending downwardly from the center of the drill bit, and applying a weight on the bit not exceeding about 500 pounds. 

2. A drill bit as set forth in claim 1 having 5 to 20 nozzles with the opening through the nozzles having a diameter in the range of three thirty-seconds to three-sixteenths inch.
 3. A drill bit as set forth in claim 1 in which bars extend downwardly from the lower surface of the drill bit at a distance less than the standoff element and are adapted to break thin rock ridges that may extend upwardly from the bottom of the borehole.
 4. A drill bit as set forth in claim 1 in which the drill bit body has a shank of smaller diameter than the drill bit body at its upper end and baffle plates extend radially from the shank.
 5. A method of drilling a borehole of a well in hard formations comprising rotatably suspending a drill bit on the lower end of drill pipe extending down the well, pumping a drilling liquid having an abrasive suspended therein down the drill string to the drill bit at a pressure of at least 4,000 p.s.i., discharging the drilling liquid from the drill bit at a velocity of at least about 650 feet per second through 5 to 20 nozzles having a diameter of three-sixteenths to three thirty-seconds inch positioned to discharge drilling liquid against substantially the entire bottom of the borehole and sloping downwardly through the lower end of the drill bit in a direction having a component in the direction opposite the direction of rotation of the drill bit whereby reaction from the drilling liquid rotates the drill bit at a rate of 500 to 2,000 r.p.m., supporting the drill bit on the bottom of the borehole by a standoff element extending downwardly from the center of the drill bit, and applying a weight on the bit not exceeding about 500 pounds. 